This investigation is interested in understanding the pathogenesis of the morphologic and biochemical lesions in the liver, skeletal muscle, heart, spleen, kidney, pancreas and other organs induced in young rats by force-feeding purified diets devoid of single essential amino acids. Some of the morphologic changes in rats force-fed for 3 to 7 days with the experimental diets resemble some of those that occur in the human disease kwashiorkor. Using this experimental model, we plan to investigate the mechanisms responsible for the biochemical and morphologic changes. Studies dealing with protein synthesis and catabolism in the liver, skeletal muscle, heart and other organs will be conducted. The role that alterations in circulating amino acids as well as in free levels of amino acids in organs play in regulating protein metabolism will be studied. Also, the role that dietary tryptophan has on the regulation of polyribosomes and protein synthesis in the liver and other organs will be investigated. Detailed studies on the changes in total, free and membrane-bound polyribosomes after dietary alterations will be conducted.